Firstly I think 4k alone is crap without HDR. Not because it’s worse than another resolution but resolution by itself isn't enough difference at normal seating distances. It's been shown to be the case in blind tests that people viewing 1080p content and normal distances don't see the shift to 4k by itself. Only when you add wide color gamut and high dynamic range do most people actually see the difference.
Were the tests done watching some popular demanding games? For example in Witcher 3 (and 2) I notice more texture detail in 4k than in 1080 sitting at the proper distance with no HDR.
So now we get to the wide color gamut consideration. That without it people wouldn't notice any difference. I'm assuming you meant that HDR doesn't have to be added. I know you said "wide color gamut
and high dynamic range" but I think in context maybe you also meant "
or high dynamic range." If you meant HDR must be added to wide color gamut then never mind this post. I'm just trying to address your wide color gamut comment as best I can.
So to continue, monitors with wide color gamut are popular and that may make it hard for me to disprove the results of the tests you described. I'd have to take the tests myself looking at games and movies on monitors without a wide color gamut vs ones with it like I assume they did in those tests. Or simply decide whether or not believe the tests you mentioned based on whatever other tests on the subject I can find on the web.
So can anyone provide a counter argument to the claim that wide color gamut is a main reason people notice a difference between 4k and 1080? Assuming HDR isn't needed. I'm hoping someone does find counter arguments since I prefer 4k. But I'm not having much luck finding such tests on Google. I know the tests have been done as mentioned above but hard to find in my casual searching. This reply is far longer than I'd like but I tend to write wordy stuff. I guess I don't have the conciseness of other posters.
And I'm still not done yet. Going back to my Witcher 2 and 3 comments and applying them to the tests that people took. I'm assuming that on monitors without wide color gamut the people did not notice any increase in detail in 4k vs 1080. Meaning the textures looked about the same in quality. Not saying I believe the results. But that's the kind of test results I was trying to find on the net. And for any counter tests to those tests.